Proper balancing of vehicle tires as well as a tire and wheel assembly is important for safety of vehicle operation and for getting the most wear from the tire. Balancers in the prior art have been divided into static and dynamic types, and while there are both types in daily use, the accuracy of each types has been put in question.
It is recognized that static balancers require the tire and wheel assembly to be removed from the vehicle and placed on a stand with the assembly in a generally horizontal position on a wobble axis so the unbalance condition will be revealed by the assembly tilting out of the horizontal. The static balancer is usually provided with a bubble to indicate when the tire and wheel assembly is in a proper horizontal or static balanced position, thereby indicating that the weight distribution around the circumference is evenly distributed when the bubble reaches a centered position. In order to center the bubble it is necessary for the operator to watch the bubble and experimentally apply a weight at various places around the periphery of the wheel rim, and to adjust the amount and position of the weight to obtain a balanced condition. The weight or weights may then be secured in position on the wheel rim. Occasionally when an excessively large single weight is required the operator will divide the amount of weight evenly and place the respective weights on opposite sides of the wheel rim on the theory that the unbalance may be on one side or the other of the tire.
Dynamic balancers are generally sub-divided into those which are operable without removing the tire and wheel from the vehicle, and those which are only operable when the tire and wheel have been removed. An example of the first type of dynamic balancers is disclosed in Hunter U.S. Pat. No. 2,662,396 issued Dec. 15, 1953, as well as Hunter U.S. Pat. No. 2,723,555 issued Nov. 15, 1955. These patents disclose balancer apparatus which must be attached to the wheel rim and are operable while the wheel and tire are in rotation to move a balancing weight to a position substantially opposite the unbalancing force, and to indicate the amount of weight needed to oppose the unbalancing force.
The second type of dynamic balancer requires the tire and wheel to be removed from the vehicle and be secured to a rotatable spindle. The rotation of the tire and wheel will generate a vibration which can be measured as to amount and direction for the purpose of selecting the amount of weight necessary to oppose the unbalancing force, as well as to locate the position for placing the balancing weight. An example of this type of dynamic balancer has been disclosed in Curchod, et al U.S. Pat. No. 3,910,121 issued Oct. 7, 1975.
Both types of dynamic balancers have advantages as well as disadvantages in that while dynamic balancing is preferred by some experts it requires careful balancing by the operator to place balancing weight in amount and location that will correct the unbalanced condition. Frequently vehicle tires have carcass material which is non-uniform and the result produces unbalance in the final tire. The non-uniformity of carcass material makes it difficult to find the place around the tire periphery for the weight which will oppose the unbalance condition and produce accurate dynamic balancing results. Generally, the type of defect in the tire construction that causes unusual or dangerous vehicle operations may be the result of uneven weight distribution in the tire body, faulty molding, belt mislocation in radial and bias-belted tires, slippage in the splices, or uneven thickness in the tire body. The problem is to correctly diagnose the defect and compensate for it by weights of the proper value located in the proper place or places.